What bird was credited with saving Rome from the Gauls in 390BC?

Greylag goose.

"An interesting fact about Greylag geese is that they were once considered sacred by the Romans after reportedly saving the city of Rome in 390 BC. When the Gauls tried to climb in, the geese warned the Romans with their loud calls about the attempted invasion. After this, Caesar believed that the geese were sacred and it was ordered that the geese were to not be eaten in Pre-Roman Britain."

http://animaldiversity.ummz.umich.edu/site/accounts/information/Anser_anser.html

I would doubt the validity of the last sentence in that quote. Caesar was about 300 years later to start with, and he only spent three months in Britain anyway. How he could order that geese not be eaten in Pre-Roman Britain is quite beyond me.... (I know it says 'it was ordered' not 'he ordered' but the Ancient Brits wouldn't have heard of this edifying tale, and wouldn't have stopped eating greylags, brents or pinkfeet as a result of it. It's another of those unchecked 'facts'. http://www.vroma.org/~bmcmanus/caesar.html